Isotactic polypropylene is an essentially linear, highly crystalline polymer. It is well known commercially for its high tensile strength, stiffness and hardness. An important use of polypropylene commercially is as filament, e.g., rope, cordage, webbing and carpeting. Relative to textiles made from nylon or polyester, however, polypropylene is deficient in resiliency and creep resistance. Resiliency is the ability of a fiber to recover from having been bent over, for example, the ability of carpet filament or staple to return to its original shape after being under a piece of furniture. Unfortunately, polypropylene fibers accept a anything except very dense carpets. Creep is the continuous elongation over an extended period of time under a load. In drapery applications, the creep of polypropylene is generally such that the fabric will undergo dimensional deformation with time. In polypropylenes used in textile applications, the same creep can lead to a loss of fabric strength.
Nylon and polyester are often favored over polypropylene in applications requiring resiliency and creep resistance. Nylon and polyester, like polypropylene, are crystalline polymers which, in their solid state, have both crystalline and amorphous phases. In contrast to polypropylene, however, nylon and polyester have considerably higher glass transition temperatures, generally about 100.degree. C. and 150.degree. C., respectively. Therefore, at normal, ambient use temperatures, the amorphous phase in polyester and nylon is effectively "frozen" and the molecular chains therein are generally prevented from stress relaxing. Polypropylene has a glass transition temperature of about 0.degree. C. At ambient temperatures it is above its glass transition temperature. Thus chains in the amorphous phase are able to move, with the result that creep and poor resiliency are manifested.
It is known from U.S. Pat. No. 3,361,849 to Cramer, et al., to employ blends of polypropylene with from about 1% to about 60% of hydrogenated hydrocarbon polymers in applications for making self-supporting film stated to possess outstanding physical properties, heat sealability, and light stability. In Example 12 of this patent, for example, there is described a film made from 80 parts of isotactic polypropylene and 20 parts of a hydrogenated hydrocarbon polymer having a softening point of 105.degree. C., an average molecular weight of about 1170, and iodine value of 25, and prepared by hydrogenating the resinous catalytic polymerization product of unsaturated monomers derived from cracked petroleum and composed essentially of dienes and reactive olefins.
It is known from U.S. Pat. No. 3,341,626 to Peterkin, to use a hot melt adhesive including a blend of atactic polypropylene, isotactic polypropylene, and terpene resins. Bonds formed by application of this hot melt adhesive composition are stated to have resistance to creep defined as the susceptibility of the bond to deform at elevated temperatures, e.g., 75.degree. C.
Hot melt adhesive blends made from polyethylene, polypropylene, and a tackifying agent are known from U.S. Pat. No. 4,076,670 to Godfrey. These adhesives are stated to have creep resistance as evaluated over the temperature range of 0.degree. F. to 35.degree. F.